xref: /freebsd/stand/uboot/arch/arm/start.S (revision 9768746b)
1/*-
2 * Copyright (c) 2008 Semihalf, Rafal Czubak
3 * All rights reserved.
4 *
5 * Redistribution and use in source and binary forms, with or without
6 * modification, are permitted provided that the following conditions
7 * are met:
8 * 1. Redistributions of source code must retain the above copyright
9 *    notice, this list of conditions and the following disclaimer.
10 * 2. Redistributions in binary form must reproduce the above copyright
11 *    notice, this list of conditions and the following disclaimer in the
12 *    documentation and/or other materials provided with the distribution.
13 *
14 * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
15 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
16 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
17 * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
18 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
19 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
20 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
21 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
22 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
23 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
24 * SUCH DAMAGE.
25 *
26 * $FreeBSD$
27 */
28
29#include <machine/asm.h>
30#include <machine/armreg.h>
31
32	.text
33	.extern	_C_LABEL(self_reloc), _C_LABEL(main)
34	.weak	_DYNAMIC
35
36/*
37 * Entry point to the loader that U-Boot passes control to.
38 */
39	.globl	_start
40_start:
41
42	mrc     p15, 0, ip, c1, c0, 0
43	orr	ip, ip, #(CPU_CONTROL_UNAL_ENABLE)
44	orr	ip, ip, #(CPU_CONTROL_AFLT_ENABLE)
45	mcr     p15, 0, ip, c1, c0, 0
46
47	/* Save the arguments and return register before calling self_reloc */
48	push	{r0, r1, r9, lr}
49
50	/*
51	 * Do self-relocation when the weak external symbol _DYNAMIC is non-NULL.
52	 * When linked as a dynamic relocatable file, the linker automatically
53	 * defines _DYNAMIC with a value that is the offset of the dynamic
54	 * relocation info section.
55	 * Note that we're still on u-boot's stack here, but the self_reloc
56	 * code uses only a couple dozen bytes of stack space.
57	 */
58	adr	ip, .here_off		/* .here_off is a symbol whose value */
59	ldr	r0, [ip]		/* is its own offset in the text seg. */
60	sub	r0, ip, r0		/* Get its pc-relative address and */
61	ldr	r1, .dynamic_off	/* subtract its value and we get */
62	teq	r1, #0			/* r0 = physaddr we were loaded at. */
63	addne	r1, r1, r0		/* r1 = dynamic section physaddr. */
64	blne	_C_LABEL(self_reloc)	/* Do reloc if _DYNAMIC is non-NULL. */
65
66	/* Restore saved arguments */
67	pop	{r0, r1, r9, lr}
68
69	/* Hint where to look for the API signature */
70	ldr	ip, =uboot_address
71	str	sp, [ip]
72
73	/* Save U-Boot's r8 and r9 for syscall trampoline */
74	ldr	ip, =saved_regs
75	str	r8, [ip, #0]		/* old gd pointer (use to hold lr) */
76	str	r9, [ip, #4]		/* new gd pointer */
77
78	/*
79	 * Start loader.  Save return address first (r8 is available from
80	 * trampoline save).
81	 */
82	mov	r8, lr
83	bl	main
84	mov	lr, r8
85
86	/* Restore U-Boot environment */
87	ldr	ip, =saved_regs
88	ldr	r8, [ip, #0]
89	ldr	r9, [ip, #4]
90	mov	pc, lr
91
92	/*
93	 * Data for self-relocation, in the text segment for pc-rel access.
94	 */
95.here_off:
96	.word	.
97.dynamic_off:
98	.word	_DYNAMIC
99
100/*
101 * syscall()
102 */
103ENTRY(syscall)
104	/* Save caller's lr, r8 and r9 */
105	ldr	ip, =saved_regs
106	str	r8, [ip, #8]
107	str	r9, [ip, #12]
108	str	lr, [ip, #16]
109	/* Restore U-Boot's r8 and r9 */
110	ldr	r8, [ip, #0]
111	ldr	r9, [ip, #4]
112	/* Call into U-Boot */
113	ldr	lr, =return_from_syscall
114	ldr	ip, =syscall_ptr
115	ldr	pc, [ip]
116return_from_syscall:
117	/* Restore loader's r8, r9 and lr */
118	ldr	ip, =saved_regs
119	ldr	lr, [ip, #16]
120	ldr	r9, [ip, #12]
121	ldr	r8, [ip, #8]
122	/* Return to caller */
123	mov	pc, lr
124
125/*
126 * Data section
127 */
128	.data
129	.align	4
130	.globl	syscall_ptr
131syscall_ptr:
132	.long	0
133
134	.globl	uboot_address
135uboot_address:
136	.long	0
137
138saved_regs:
139	.long	0	/* U-Boot's r8 */
140	.long	0	/* U-Boot's r9 */
141	.long	0	/* Loader's r8 */
142	.long	0	/* Loader's r9 */
143	.long	0	/* Loader's lr */
144